1. Field of the Invention
This invention relates to broadcasting digitally modulated signals and an analog signal within the same frequency channel assignment, and more particularly to receiver addressable digital broadcasting techniques.
2. Description of the Related Art
There has been increasing interest in the possibility of broadcasting digitally encoded audio signals to provide improved audio fidelity. Several approaches have been suggested. One method simultaneously broadcasts analog and digital signals in a standard AM broadcasting channel. An amplitude modulated radio frequency signal having a first frequency spectrum is broadcast. The amplitude modulated radio frequency signal includes a first carrier modulated by an analog program signal. Simultaneously, a plurality of digitally modulated carrier signals are broadcast within a bandwidth which encompasses the first frequency spectrum. Each of the digitally modulated carrier signals is modulated by a portion of a digital program signal. A first group of the digitally modulated carrier signals lies within the first frequency spectrum and is modulated in quadrature with the first carrier signal. Second and third groups of the digitally modulated carrier signals lie outside of the first frequency spectrum and are modulated both in-phase and in-quadrature with the first carrier signal. Both transmitters and receivers are provided in accordance with that method.
The waveform in such an AM compatible digital broadcasting system has been formulated to employ multiple digital carriers to carry a composite data rate suitable for high quality audio reproduction.
It is desired to transfer broadcast program material concurrently with destination specific information permitting the transmission of messages to a preselected receiver(s). For example, paging systems are increasingly popular for relaying destination specific messages and other information. Therefore, there is a need for a broadcasting system which transmits digitally encoded audio signals for improved audio fidelity and has detector addressable capabilities for transmitting receiver specific information.
The invention solves this need by providing for a receiver addressable AM compatible digital broadcast system.